Troubleshooting Notes #2

Survivable endpoints: IP Phones and MGCP Gateways

Nonsurvivable endpoints: H.323 Gateways, SCCP Gateways, CTI/TAPI Endpoints

The rules for call survivability can be summarized as follows:

• If the call involves nonsurvivable endpoints, and a CallManager involved in the call fails, the call fails.
• If the call involves one nonsurvivable endpoint and one survivable endpoint, the call fails only if the CallManager that the nonsurvivable endpoint is registered to fails.
• If the call involves only survivable endpoints, and one or more CallManagers involved in the call fails, the streaming connection between the endpoints is maintained. Note, however, that the endpoints do not have supplementary services available to them after the failure.
• If a hardware-based conference bridge is involved in a call, and the CallManager controlling the conference bridge fails, all calls from nonsurvivable endpoints fail. All calls from survivable endpoints continue in the conference.

  If a software-based conference bridge is involved in a call and the CallManager controlling the conference bridge fails, all calls from the nonsurvivable endpoints fail. All calls from survivable endpoints continue in the conference until the party terminates the call voluntarily. The conference bridge reregisters with an available CallManager.

• If the call involves an MTP or a transcoder, the call fails.
• If the call is in the and a CallManager involved in the call fails, the call fails.

The IP Voice Media Streaming
Application supports only G.711 µ-law and G.711 A-law codecs. It can provide up to 128 streams of conferencing on a standalone server or 24 streams when it coresides with CallManager on the same server.onf

Conference Bridges, Transcoders, and MTPs: Best Practices

• When a media resource is assigned to any MRG, it is no longer available as part of the default MRGL. This means that endpoints that require the use of a media resource in an MRG must have an MRGL configured that contains that MRG.
• Be extremely careful when configuring your codec selections between regions. This is by far the most common cause of transcoder problems.

Troubleshooting MOH

1. Check the MOH server registration status.
2. Check the MRG and MRGL configuration.
3. Verify router configuration for multicast (if multicast is used).
   ip multicast-routing
   ip pim sparse-mode | ip pim dense-mode
4. Verify the multicast capability of the terminating voice gateway.
5. Verify the codec used by all devices involved.
6. Verify the location’s configuration if you are using the centralized call processing model.

H.225/H.245 Summary

H.225 RAS Signaling:

• RAS is the signaling protocol used between gateways and gatekeepers. The RAS channel is opened before any other channel and is independent of the call setup and media transport channels.
• RAS uses User Datagram Protocol UDP 1719 (H.225 RAS messages) and UDP 1718 (multicast gatekeeper discovery).

H.225 Call Control (Setup) Signaling

• H.225 call control signaling is used to setup connections between H.323 endpoints.
• A reliable (TCP) call control channel is created across an IP network on TCP 1720. This port initiates the Q.931 call control messages for the purpose of the connection, maintenance, and disconnection of calls.

H.245 Media Control and Transport

• H.245 handles end-to-end control messages between H.323 entities.
• H.245 procedures establish logical channels for transmission of control channel information.
• It is used to negotiate channel usage and capabilities such as flow control and capabilities exchange messages.